Sunpath for leap years

Nathaniel · September 29, 2023, 3:47pm

Is there a way, using or modifying the Sunpath component, to get sun direction vectors for leap years and other years? What I would like to do is show that the vector for noon on Feb 28, 2027 is slightly different from the same day in 2026 or 2028.

mostapha · September 29, 2023, 8:10pm

Hi @Nathaniel, It is possible to get them for the leap_year but it is not exposed in the UI. You have to change the components in two places:

In the LB Calculate HOY component change line 43 to calculate pass leap_year=True to create the DateTime for the leap year.
In the LB SunPath component, set is_leap_year to True after creating the sunpath. Line 245 in the above screenshot.

Here is the edited GH file.

Changing the year is a bit more work since it is hard-coded in the source code. We use 2016 for leap_year and 2017 for a typical year.

github.com

ladybug-tools/ladybug/blob/e70767b655e0c62da2efdf73cbb966d6ae3929d6/ladybug/dt.py#L42


      
              * float_hour
              * tzinfo
              * year
          """
          
          __slots__ = ()
          
          def __new__(cls, month=1, day=1, hour=0, minute=0, leap_year=False):
              """Create Ladybug datetime.
              """
              year = 2016 if leap_year else 2017
              hour, minute = Time._calculate_hour_and_minute(hour + minute / 60.0)
              try:
                  return datetime.__new__(cls, year, month, day, hour, minute)
              except ValueError as e:
                  raise ValueError("{}:\n\t({}/{}@{}:{})(m/d@h:m)".format(
                      e, month, day, hour, minute
                  ))
          
          def __reduce_ex__(self, protocol):
              """Call the __new__() constructor when the class instance is unpickled.

You can manually edit the source code in the C:\Program Files\ladybug_tools\python\Lib\site-packages\ladybug\dt.py to change the years to the two that you are interested in comparing. Don’t forget to Restart Rhino to reload the libraries after editing them.

Nathaniel · October 4, 2023, 1:15pm

@mostapha’s solution worked. There are multiple places in dt.py (and sunpath.py) where the year is hard coded, so I created global variables for the leapyear year and the non-leapyear year. I also implemented a check in Grasshopper that throws an error if the year I’m processing doesn’t match one of those global variables. I was then able to produce analemmas for four consecutive years showing the differences in solar angles, only needing to restart Rhino twice to reset the global variables.

mostapha · October 4, 2023, 1:41pm

Thank you for the update, @Nathaniel! And glad that you figured it out. Maybe we should consider exposing this as a variable at some point to make it easier for cases like yours.